A major problem associated with producing wells of oil and gas is the increased water coning. In most reservoirs, oil is produced from an oil zone which often lies over a water zone and beneath a gas zone. During production of oil from a well, water underlying the oil zone may flow strongly upward into the lower pressure zone around the well and into the well to the oil zone level. Because the water is generally lower in viscosity than oil, the water may flow more rapidly than the oil and create a water zone around the well substantially inhibiting the entry of oil into the well. This water coning is especially serious in reservoirs which is subject to a bottom water drive.
Gas-coning may also happen during oil production. This cause is a reduction in oil production resulting in an increase in gas:oil ratio. The downward flow of the lower viscosity gas into the oil zone around the production well interferes with the flow of oil into the wellbore.
Several references provide somewhat limited solutions to the above described problems. For example, U.S. Pat. No. 3,866,682 discloses controlling water and gas coning by forming a barrier having a shape like a hollow frustum in a production well. U.S. Pat. No. 3,404,734 discloses in-situ production of gels for plugging water coning. Additionally, U.S. Pat. No. 4,485,875 discloses in-situ production of gels by injecting a solution mixture of polyacrylamide, phenol and an aldehyde to selectively plug permeable zones. Moreover, U.S. Pat. No. 3,695,356 discloses a controlling mechanism by hydrolysis of gels formed by injecting water soluble, gel-forming materials. Furthermore, U.S. Pat. No. 4,418,755 discloses inhibiting water flow by injecting a gelling agent into the formation.
Finally, it is well-known that, as disclosed in Water-Soluble Polymers for Petroleum Recovery (G. A. Stahl and D. N. Schulz, editors, Plennum Press, New York, N.Y., 1988), pp. 299-312, a gelable polymer is most commonly used to divert the flow from the high permeability zones and fractures to the unswept oil-containing portions of the reservoirs. For example, in the gelation of a gelable water soluble polymer, an aldehyde is condensed with a phenolic compound along with the polymer injected into the reservoir to form gels. The gels thus formed can reduce the permeability and divert the flow of injected fluids resulting in enhanced oil recovery.
However, none of the above described references disclose the use of gellable mixtures having different buoyancies relative to the brines of the reservoirs to control the location in the reservoirs where the gels are formed. The control of such gelation would more effectively block water coning allowing the entry of oil into the well for recovery. Gelling solutions with densities lower than oil can be injected in producing wells with gas-coning problems to float on top and produce a gel at the interface to block gas coning.